Frozen confections which consist of ice cream, frozen yoghurt, water ice or the like coated with chocolate, frozen fruit juice, or other coatings are popular products. These products are often supported on a stick so that they can be conveniently consumed without being held directly, thus avoiding the consumer's fingers becoming covered with the coating.
Chocolate coated stick products are one example of this type of product that has been known for many years. They are usually produced by an “extrude and cut” process, as follows. Ice cream from the freezer is extruded vertically downwards though a nozzle onto a conveyor. Sticks are inserted as the ice cream comes out of the nozzle and a heated wire cuts it horizontally into uniform portions of the required thickness. While the aim is to insert sticks parallel to the cut surface of the ice cream and in the middle of the portion, in practice sticks are often slightly misplaced or misaligned. The conveyor carries the ice cream through a hardening tunnel where its temperature is reduced to about −25° C. After the ice cream leaves the hardening tunnel, its stick is picked up by a stick gripper. The stick gripper consists of sets of tongs mounted on a carriage frame. Molten chocolate is held in a dipping tank at about 45° C. The stick gripper transfers the ice cream to the dipping tank, where it is lowered into the liquid chocolate for a certain time, and then removed. After dipping, the chocolate begins to solidify on the cold ice cream. Within a few seconds the liquid chocolate becomes dry to the touch and has plastic or leathery texture. This arises from partial crystallization of the fat. Crystallization continues slowly, and it typically takes at least several hours for the chocolate to become brittle (i.e. it cracks when deformed).
The shape and/or surface appearance of such products is a significant factor in their appeal to consumers. Efforts have therefore been made to find methods for making products having an image or logo embossed upon them. WO 02/052944 describes an embossing device and a method for embossing characters or structures onto frozen confectionery articles by means of a metal stamp at a temperature of between 0 and 60° C. The embossed frozen confection may then be coated with chocolate. However since coating occurs after stamping, fine details of the stamped pattern are lost because the chocolate covers them up. This process is therefore only suitable for large and simple structures, and in particular it is not suitable for structures below about 3 mm in size. Similarly, the embossing depth must be at least about 4 mm.
WO 02/078460 describes an alternative process in which the ice cream is first shaped in a mould and a stick is inserted, then it is coated, for example in chocolate, hardened and then formed (i.e. moulded or stamped) a second time to produce the final shape. Since forming takes place after coating, the problem associated with the method of WO 02/052944 is avoided and small details can be produced on the product surface. However, the two forming steps makes this process complex and slow.
Therefore there remains a need for a simple process for embossing a pattern with improved feature definition onto a coated frozen confection product. There is also a particular need for a process for embossing a pattern with improved feature definition onto coated frozen confections produced using “extrude and cut” type processes.
Tests and Definitions
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art (e.g. in frozen food manufacture). Definitions and descriptions of various terms and techniques used in frozen confectionery manufacture are found in “Ice Cream”, 6th Edition R. T. Marshall, H. D. Goff and R. W. Hartel, Kluwer Academic/Plenum Publishers, New York 2003.
Frozen confection means a confection made by freezing a pasteurised mix of ingredients such as water, fat, sweetener, protein (normally milk proteins), and optionally other ingredients such as emulsifiers, stabilisers, colours and flavours. Frozen confections may be aerated. Frozen confections include ice cream, water ice, frozen yoghurt and the like.
Coating means any edible material which can be used to form a coating layer on a frozen confection. Coatings include chocolate (dark chocolate, white chocolate, milk chocolate), chocolate analogues which are made using fats other than cocoa butter (for example coconut oil), and fruit purees. Coatings are applied to the frozen confection as liquids, but solidify when they are cooled down, for example as a result of contact with the frozen confection. Chocolate and chocolate analogues have complex solidification behaviour because they contain mixtures of different triglycerides which can crystallize in different forms. For example, cocoa butter can exist in six different crystalline forms (polymorphs). As chocolate solidifies, triglycerides begin to crystallize. Within a few seconds the chocolate becomes dry to the touch and has plastic or leathery texture. Crystallization continues slowly, so that it typically takes several hours or days for the to triglycerides to fully crystallize and so that the chocolate reaches its maximum brittleness. Chocolate analogues made from fats other than cocoa butter display similar behaviour to chocolate, but typically crystallize over a narrower temperature range and reach maximum brittleness more quickly than chocolate. In this context, “liquid” means that the coating can flow. “Liquid” does not include coatings in a plastic state when they are deformable, but do not flow.
Stamping Surface
The stamping surface means the surface that makes contact with the coated frozen confection and thereby embosses a pattern onto it. Typically the stamping surface consists of a flat base with raised and/or indented features which form a negative of the desired pattern (i.e. raised features in the stamping surface correspond to depressions in the embossed pattern). Thus, it will be understood that it is the flat base that defines the alignment of stamping surface in relation to the coated frozen confection. It is also possible that the base is not flat, e.g. it is convex, so that the embossed feature is basically concave, with further raised or lowered features. In this case the stamping surface is aligned with the surface of the coated frozen confection when the normal to the centre of the stamping surface is perpendicular to the surface of the coated frozen confection.
Resilient Mounting
A resilient mounting means a mounting which:                (a) allows the stamp to move (relative to the support) linearly in the direction perpendicular to stamping surface, and to tilt about any axis lying in the plane of the stamping surface when it comes into contact with the surface of the coated frozen confection; and        (b) applies a restoring force so that the stamp returns to its initial position (relative to the support) when the stamping surface is removed from the surface of the coated frozen confection.        
Spring constant (in units of Newtons per millimeter) means the force (in Newtons) that must applied to extend a spring by one millimeter.
Method for Measuring the Temperature of the Stamping Surface
The temperature of a stamping surface is measured using an Agema Thermovision 570 thermal camera (according to the manufacturer's instructions).
We have developed a simple process for stamping a pattern with small features onto a coated frozen confection product. Accordingly, in a first aspect, the present invention provides a process for stamping a pattern onto a coated frozen confection comprising the steps of:                a) at least partially covering the frozen confection with a layer of coating; and        b) bringing a stamping surface into contact with the coated frozen confection;characterised in that in step (b) the coating is liquid.        
We have found that it is possible to stamp the product while the coating is still liquid, thus providing very high definition surface features, avoiding the risk of the coating cracking during the stamping step and lowering the force required for stamping. Since stamping takes place after the frozen confection has been coated with chocolate, the problems of poor surface definition associated with coating after stamping are avoided. This process provides a simple method of producing attractive coated products. In this aspect, the invention applies to any coated frozen confection product, for example enrobed ice cream bars, and not only to stick products.
In the extrude and cut process, small errors in stick position (so that the stick is not in exactly the centre of thickness of the cut ice cream) and orientation (so that the stick is slightly twisted with respect to the cut ice cream) are common. Subsequent stamping of the product is difficult because although the position of the stick can be accurately controlled in relation to the stamp, the surface of the coated product to be stamped may be too close, too far away from, or tilted with respect to the correct position. As a result, the embossed pattern may be too shallow (so poorly defined), too deep (so that the stamp penetrates through the coating and reaches the ice cream) or uneven (so that it is deeper at one edge of the stamp than the other). We have developed a process which overcomes the limitations of “extrude and cut” type processes when it is desired to stamp a pattern onto a coated frozen confection.
Accordingly, the process of the present invention preferably further comprises, before steps (a) and (b) the steps of:                (i) extruding the frozen confection from a nozzle;        (ii) inserting a stick into the frozen confection;        (iii) cutting the frozen confection into pieces;wherein steps (ii) and (iii) take place simultaneously or in either order during step (i); and then subsequently        (iv) handling the frozen confection by the stick;wherein the stamping surface is resiliently mounted on a support.        
We have found that when the stamping surface is resiliently mounted on a support it positions and aligns itself with respect to the surface to be stamped as it they come into contact. Therefore the pattern is embossed correctly even when the surface to be stamped is initially incorrectly positioned or misaligned. Preferably the stamping surface is resiliently mounted on the support by a single resilient means. More preferably the single resilient means comprises a spring. Most preferably the spring has a spring constant of from 0.1 to 0.5 N/mm.
Preferably step (b) takes place from 1 to 10 seconds, more preferably from 1 to 6 seconds, most preferably from 2 to 4 seconds after step (a).
Preferably the stamping surface is at a temperature of below −5° C. in step (b). More preferably the stamping surface is at a temperature of between −5° C. and −100° C., most preferably between −10° C. and −80° C. in step (b).
Preferably the thickness of the coating layer is from 0.5 to 5 mm, more preferably from 1 to 3 mm.
Preferably the coating is chocolate or a chocolate analogue. Most preferably the coating is chocolate.
Preferably the frozen confection is ice cream.
Preferably the stamping surface comprises features with a height of from 0.5 to 1.5 mm.
In a second aspect, the present invention provides an apparatus for stamping a pattern onto a coated frozen confection comprising:                a) a means for holding the frozen confection;        b) a stamp, comprising a stamping surface, mounted on a support; and        c) a means for moving the support so that the stamping surface can be brought into contact with the surface of the frozen confection;characterised in that the stamp is mounted on the support by a resilient mounting.        
Preferably the resilient mounting comprises a single resilient means. More preferably the single resilient means comprises a spring. Most preferably the spring has a spring constant of from 0.1 to 0.5 N/mm.
Preferably the stamp is made from aluminium or stainless steel.
Preferably the stamp has a mass of from 1 to 20 g, more preferably from 2 to 10 g, most preferably from 3 to 7 g.
Preferably the stamping surface has an area of from 25 to 2500 mm2, preferably from 100 to 900 mm2.